Mod C Unit 2 Lesson 2 - Resource Availability

The graph shows the population of a group of rabbits in a restricted area studied over a period of five years. Which statement might explain why the population leveled off as shown in the graph?

• The resources in the area ran out.

• The rabbits encountered a new disease.

• Predators were introduced into the area.

• Competition for resources limited the rabbit population.

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Which of these events would lead to an increase in the size of a population of squirrels?

• More squirrels are born than die.

• Some squirrels emigrate in search of food.

• New predators are added to the ecosystem.

• A large number of squirrels die because of a forest fire.

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Which of these is the most likely reason that a population in an ecosystem could have a sharp decline?

• The number of prey suddenly increases.

• The number of predators suddenly decreases.

• The competition for the same resource suddenly drops.

• The abiotic resources in the environment suddenly drops.

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Without other changes to a population, which of these will cause a population to increase in size?

• The birth rate equals the death rate.

• The birth rate is less than the death rate.

• The birth rate is greater than the death rate.

• The birth rate and the death rate both equal zero.

How did the drought most likely affect populations of grasshoppers living in the grassland ecosystems?

• The insects adapted to eat other available foods instead of grass.

• Populations increased because other insects were eliminated from the environment.

• Populations decreased because the resources the grasshoppers needed were not available.

• Populations of grasshoppers were not affected because the size of a population cannot change over time.

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How did the drought most likely affect the carrying capacity for populations of farm animals?

• The populations increased at first and then decreased as time went on.

• The populations decreased because the environment no longer had enough resources.

• The populations stayed the same because they depended on biotic factors, not abiotic factors.

• The populations increased because there was more room for animals once the plants were gone from the environment.

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Aphids are tiny bugs that most people consider garden pests. They feed on plants and can damage them. Ladybugs are predators of aphids. Which graph best displays the general relationship between ladybug and aphid populations in a garden?

• 
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Answer explanation

This is correct because predator and prey populations would have a positive correlation. The more aphids there are, the more ladybugs could be supported by the available prey.

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Fragilaria is a type of algae found in many bodies of fresh water. Daphnia are small crustaceans that feed on the algae. The graph shows growth rates of Fragilaria at different temperatures of water. Based on this graph, predict what would happen to the Daphnia population during a very hot summer.

• The Daphnia population would increase because the Fragilaria population would increase.

• The Daphnia population would increase because the Fragilaria population would decrease.

• The Daphnia population would decrease because the Fragilaria population would decrease.

• The Daphnia population would decrease because the Fragilaria population would increase.

Answer explanation

The Daphnia population would decrease because the Fragilaria population would decrease.

This is correct because the Fragilaria population would decrease in hot weather. Since Daphnia depend on them for food, their population would also decrease.

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Drought is a weather condition that may limit the amount of water resources available to an ecosystem. Which of the following may be one result of drought?

• Fish populations may decline due to lower river levels.

• Birds may not build nests due to temperature change.

• Flowering plants may produce more seeds due to lack of water.

• Predator populations may increase due to increased prey populations.

Answer explanation

Fish populations may decline due to lower river levels.

This is correct because a drought may reduce water levels.

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Walruses use sea ice as a diving platform to feed on clams on the sea floor. What prediction can be made about sea ice cover in the year 2020 and how will it impact walruses?

• The ice cover will increase and walrus populations will grow.

• The ice cover will continue to decrease and walrus populations will decline.

• The ice cover will continue to decrease but walruses will move to new areas and populations will grow.

• The ice cover will increase but there will not be enough space for walruses to live.

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